Given a binary tree, find its minimum depth.
The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node.
Note: A leaf is a node with no children.
Input: root = [3,9,20,null,null,15,7] Output: 2
Input: root = [2,null,3,null,4,null,5,null,6] Output: 5
- The number of nodes in the tree is in the range
-1000 <= Node.val <= 1000
The definition for a binary tree node
The solution in Java code
First we need to make sure that we catch our 2 edge cases:
- root is null
- root has no child nodes
Then we can check if left is null, it means that we can run the depth again, but with right, adding 1 level.
The same then applies to the right node.
Once this recursion is out, we make sure to use the built-in
Math.min() to do the same logic if not caught above:
- minimum value will be the left node under recursion
- compared to the right node under recursion
Making sure to increment our final output by 1, as we have not yet counted in the additional level yet.